The Basel III reform raised banks’ capital requirement per risk-weighted assets considerably, while risk weights were largely unchanged. This column uses a simple model to explore whether these risk weights discourage productive business investments. The model shows that when firms face collateral constraints, the optimal risk weights on corporate loans should be ‘flatter’ than they are at present. A quantitative assessment, however, suggests that welfare losses from the current system may not be large.

Subprime mortgages account for less than 1% of the world’s debt stock. How could they cause the greatest financial crisis in modern times? “Risk sensitivity” is this column’s answer. Regulators gave bankers incentives to combine bad loans with good ones and securitise the package in complex structures. The inseparability of the suspect parts meant problems with one package questioned the value of all packages. The least liquid banks failed, triggering a vicious cycle of fear and failure.